Conventional semiconductor photocathodes are described in the U.S. Pat. No. 3,958,143, U.S. Pat. No. 5,047,821, U.S. Pat. No. 5,680,007 and U.S. Pat. No. 6,002,141. Such semiconductor photocathodes are provided with a light-absorbing layer formed from a compound semiconductor which absorbs infrared rays and emits electrons among carriers generated in response to the absorption of infrared rays through an electron transfer layer (an electron emission layer) into a vacuum.